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Simulators >> AMS Simulators >> simulated time overflow
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Message started by nanopaw on Jan 29^th, 2010, 10:38am

Title: simulated time overflow
Post by nanopaw on Jan 29^th, 2010, 10:38am

I am running a simulation with a stop time of 20 ks (That's right kiloseconds) to model a process that can take minutes or hours. However, there seems to be an upper limit on the length of a Cadence AMS simulation. It gives me the following error whenever it encounters a simulation time beyond 2^63 fs.

Error! simulated time overflow
File: ./ihnl/<proj>/<cell>/verilogams/verilog.vams, line = 67, pos = 1
Scope: <testbench>.I0
Time: 9223372036 US + 0

You can tell here my precision is set to 1us, but I get the same error whenever I try to exceed 9.22 ks no matter what precision I choose with the `timescale directive.

Maybe it stores values for time in terms of femptoseconds, and it's choking on too big an exponent. It seems like there should be a way to change the base time unit.

Any ideas?

Title: Re: simulated time overflow
Post by Andrew Beckett on Feb 2^nd, 2010, 11:33am

I found an old solution http://sourcelink.cadence.com/docs/db/kdb/2001/Jan/1840958.html which says that the internal resolution in ncsim is in fs. Lots of service requests referring to this solution, which was based on feedback from someone in R&D 10 years ago. I've not seen much in the way of new requests to increase it or control it.

So it may be possible, but I'd suggest you contact Cadence Customer Support and ask for an enhancement request to adjust the internal timescale resolution - maybe it's even possible already (I don't know). This isn't really an AMS issue, but an issue with ncsim.

Regards,

Andrew.